Advise for Galvanized Steel
 

We recently got a local sheet metal company to donate their scrap metal to us. They have 3003 aluminum but not a large amounts. Most of what they can give us would be galvanized steel and I wanted to know what most people would use it for. I was also wondering about any suggestions on machining it and what other types of tooling to use as well as safety. From looking at the scrap I saw everything from angle to strips to sheets as big as 4'x4'.

Re: Advise for Galvanized Steel
 

Don't weld it.

You can get zinc poisoning from the fumes.

Re: Advise for Galvanized Steel
 

I repeat: Do not weld it.

Machining: My best recommendation is to speak with the sheet metal company, THEY work with this stuff all day, every day: Surely they know how to machine it.

In general, it is steel. Cut it with a hacksaw (or metal-cutting band saw), file it, sand it, drill it. Cut thin sheets with tin snips or aviation shears or a nibbler (manual or electric or pneumatic). Bend it, solder it (silver solder recommended, not brazing), rivet it. All are fine.

It should not come into contact with copper, which will cause electrolysis.

On a robot, some steel can be useful, but often it can be too heavy.

Re: Advise for Galvanized Steel
 

I don't get why not to put copper with steel. I connect copper to steel, once in a while! :confused:
By you saying "electrolysis," do you mean that it will break up water when you electrolyze it and place it inside water?

Re: Advise for Galvanized Steel
 

I always cringe when new people are jumped on for spreading misinformation... but I feel that this is a time for learning as well.

You can weld galvanized steel with no issues as long as you use proper equipment. You do not get zinc poisoning from the fumes. However, you should have adequate ventilation (read as borderline too much ventilation) and proper equipment (i.e. respirator) to avoid zinc oxide irritation which is similar to an allergic reaction that results in what is known as "metal fume fever." It is greatly unpleasant and has symptoms like the common flu. Fever, chills, awful headaches, and other not so fun issues commonly arise. These symptoms will be horribly uncomfortable, but generally clear up in 6-10 hours. If zinc oxide was so bad, we probably wouldn't rub it all over our bodies every summer. Most cases of major problems from welding galvanized steel are generally related to people who develop pneumonia or already have a weak respiratory or immune system, or where a person was so engulfed in fumes that the building was evacuated for visibility issues due to burning coatings of to prep for welding operations.

If what was said above was true, then stainless steel should really never be welded because it releases chromium. And that stuff is a carcinogen, damages your kidneys, and will kill you if you are exposed to it for too long.

I'm not advocating that every team go out and use galvanized steel on their robot and weld away, but making it sound like the world will end if you do is over the top a bit. In fact, to avoid any issues that could arise, it's probably smart to try to avoid it. The discomfort you will feel if you aren't right about your ventilation isn't worth the end result. Also, in the process of burning off the zinc coating, you will contaminate your weld resulting in a weak bead when using the most common welding alloys and shielding gases.

Steel also is heavy, but you generally can use a lot less of it than aluminum. To get the same strength you need thicker or more aluminum than you would steel. This company has a pretty good explanation of what I'm getting at. To say that you should always use aluminum is like saying you should only ever turn right in a car because it is easier. We have found that in using steel for a frame: it is stiffer, lighter or equal in weight (because we use less material), smaller in volume, and if it gets bent somehow we just bend it back.

Re: Advise for Galvanized Steel
 

I will have to agree with that. It scared me when I read, "you will get zinc poisoning by welding galvanized steel" because this is a type of steel. Many times, you will find steel welded, like in cars. I will have to agree with MrBasse that aluminum is much better on FRC robots. Unless the part is a very important structural part, like a climber hook, make it out of Aluminum. Not only is Aluminum less dense, but it has a greater corrosion resistance, because it is already aluminum oxide, at least on the outside. As long as space isn't an issue, aluminum will help you work through the metal and strengthen where needed and weaken where needed, because you need three times the amount of steel!

I am just wondering: would machining any of these materials cause any problems? Will there be any fine and dangerous dust in the air that could harm you? This is one of the reason why I am scared of machining (other than zombie machines coming to life and attacking us:D).

Re: Advise for Galvanized Steel
 

Well for one I don't worry too much about difficulty of machining as anything I get would be sheet metal thicknesses. As for safety, zinc dust, steel dust, aluminum powder, all can be harmful and you take the same precautions for all of them. Ventilate and protect your lungs. I doubt they like aluminum powder.::safety::

Also on weight, personally I've not had a problem. Our 2012 bot (photo attached) was 109. Our robot this past season (a 4.5' tall FCS with a 10pt climb) was 98lbs at inspection. We needed to add weight.

Re: Advise for Galvanized Steel
 

Or... grind off the galvanized coating first before welding. But then it's not galvanized steel anymore.

The reason I stated here to not weld it is because in the decision tree of pursuing things that have negative consequences, taking actions to avoid the situation should ALWAYS come before taking steps to mitigate the problem. Zinc poisoning / metal fume fever are just semantics for the same result - you can easily get sick if you do this action.

Even worse, is that people who may have a cursory knowledge of welding may not realize that they need to do anything different when welding galvanized steel, and won't realize until too late. This is the same reason why I will recommend to everyone to never laser cut polycarbonate, since avoiding dangerous fumes in the first place is better than dealing with the consequences.

Since FRC robots aren't generally subjected to salt bath/sppray tests or acidic or super humid environments, there aren't really any compelling reasons to use galvanized steel over regular steel or aluminum or polycarbonate etc., especially when a light oil coating can keep your regular steel from rusting.

And yes, while zinc oxide itself is safe in most applications (even noted by the FDA as "generally recognized as safe"), it's the fumes that are dangerous. Technically water fits this same description.

There is nothing wrong with welding steel, it's welding galvanized steel that you have to take extra precautions on. Galvanized steel is just any normal steel alloy that is coated in zinc to have better anti-corrosion properties (e.g. not rust).

Re: Advise for Galvanized Steel
 

Except that its free.

Also I assume it would be okay to water jet it?

Re: Advise for Galvanized Steel
 

This discussion is not about steel in general, it is about steel that has been specifically Galvanized. Though I would not recommend inhaling any kind of metal (or wood or plastic for that matter). You are obviously not going to die while being in the same room as a metal being machined, as all of us are still living (though only by satisfying our addiction to robots). Also, steel is heavy (EDIT: dense) it does not form dust very well.

Re: Advise for Galvanized Steel
 

Anybody good enough to weld sheet metal should already know not to breathe any welding fumes. Which means only weld in well ventilated areas. Good practice is to remove all coatings from the weld zone so you don't contaminate the weld. Zinc fumes have unpleasant short term effects which is a good enough reason to avoid them. Long term effects have not been documented which is different than no long term effects.

To avoid fuming the zinc you only have to remove it from the heat effected zone. Not really an issue here since you are using it for its cost property (free) not corrosion resistance. (Unless this is a devious game hint) Salt water game!!

Re: Advise for Galvanized Steel
 

Don't forget about the air all around you. There's water in it too ;)


When using any new material, find the MSDS. I found a galvanized sheet steel MSDS here that addresses the zinc oxide inhalation hazard.

Re: Advise for Galvanized Steel
 

...like multi-vitamins with minerals for example :) ... check the label.

Yes, do not inhale superheated steam.

Re: Advise for Galvanized Steel
 

Let's just end this argument about whether zinc fumes are dangerous. Let's just say, zinc oxide can be dangerous, but isn't always, so just make sure to have proper ventilation.

It's never bad to be overcautious, especially when you can be harmed severely, or maybe even killed. That's why we give safety tests to students before they can use tools!

Re: Advise for Galvanized Steel
 

Just a fan will get you into dealing with all of the symptoms I listed earlier. To avoid a lot of discomfort you need a dedicated welding ventilation system and most likely a respirator for any residual fumes that get past the ventilation system.

Re: Advise for Galvanized Steel
 

(Emphasis mine)

Please, if you don't actually know what you're talking about, don't offer safety advice on the subject.

I'm a professional machinist, so I handle safety concerns regarding our machine shop. I'm not a professional electrician or electrical engineer, so it's not a very good idea for me to give out safety advice about electricity besides "Don't touch it". Misinformation can cause accidents.

For this same reason, people will give out the advice; "Don't weld galvinized steel". Even though, as others have pointed out; it can be done. But it can only be done if you really, really know what you're doing. But "Don't do it" is a pretty good rule if you don't know exactly how to do it.

A fan blowing air out of the room to the outside is pretty much the bare minimum for ventilation. It might cut it if you want to get rid of some paint fumes, but when you're dealing with fumes that are actually dangerous, it's not going to be good enough.

Re: Advise for Galvanized Steel
 

Please don't guess when health and safety are involved. You don't yet have the experience and expertise to give such advice...

Have you had any training involving the welding of galvanized steel? If not, I urge you to hold your tongue when you get the urge to answer safety-related questions about it. But please keep asking questions!

[edit]I didn't see Evan's note above when I wrote my reply, and I apologize for the redundant message. I didn't delete it, because I think my final sentence is important.[/edit]

Re: Advise for Galvanized Steel
 

Here is a fact sheet from the the American Welding Society on metal fume fever. Google is you friend.

Re: Advise for Galvanized Steel
 

As a welder I prefer to TIG-braze galvanized steel with silicon-bronze filler material. I find it results in a strong weld joint and greatly reduces the amount of noxious fumes emitted by the joining process due to the low heat input of brazing and the fact that the base steel isn't actually melted. Several critical parts on our 2013 climbing mechanism were TIG-brazed with silicon-bronze filler.

Others have done a great job of addressing the safety concerns.

Re: Advise for Galvanized Steel
 

Coming back to the original post...

Remember that steel is as strong as aluminum per pound. To accomplish the same task will require the same weight of either metal. With that said, aluminum is usually a better choice because (let's face it), we're building relatively low-weight robots compared to industry. Steel is (mostly) harder to machine than aluminum (slower feed rates, smaller cuts, etc).

For machining it, the machine is as important as the tooling. Although a drill press will work, I'd advise a mill for the improved control and precision. For safety, if you're not cooking it (see previous posts), it's (mostly) just like machining regular steel.

Personally, I'd advise my team against the galvanized steel in large quantities. We'd never go through enough of it to justify the hassle of storing it and machining it. Plus, we're always running close to the weight limits and steel would just make that worse.

Re: Advise for Galvanized Steel
 

Not true as a general proposition. Depends on the type of steel, and type of aluminum being compared.

Re: Advise for Galvanized Steel
 

Can you weld galvanized steel?

Yes.

Would I feel comfortable doing it around or with high school students?

No.

Re: Advise for Galvanized Steel
 

Not true. Aluminum (as a generalization for FRC, you can find exceptions) has a significantly higher strength to weight than steel. In fact, for shafts/gears, your 7075 aluminum is both lighter and stronger that the common stainless steels places like andymark use. In terms of ultimate yield strength, aluminum is roughly 1/3 the weight and almost twice as strong.

Re: Advise for Galvanized Steel
 

I wouldn't say "significantly stronger" but yeah, it can be stronger per unit of weight.

Re: Advise for Galvanized Steel
 

It's also a more expensive. Something else to note is that steel generally is more stiff than aluminum per unit weight. When you're building something like a bridge, those two factors can be important.

The real reason aluminum is thought of as lighter (for FRC purposes) is that we rarely design on weight, we usually design on size. There's a lot of arbitrary standards in FRC (1/4" thick bearings, 20 DP gears, 2x1 tubing, etc) where stuff just needs to be that big to conform to a standard. Your WCD will be a ton harder to design if you choose .75x.75 steel tubing vs alu 2x1, for example. Also, for stuff like shafts, aluminum (especially 7075) usually has an adequate total yield strength, and since the shaft needs to be 1/2" hex, the alu will be a lot lighter than steel. In other places, we need certain plate thickenesses to get the right number of threads in a tapped hope. Again, steel will be heavier because we just care about overall thickness, not strength. Of course, if we designed all our parts to just be a certain strength, steel and aluminum would be a lot more comparable in terms of weight.

Sure, we could crazily pocket steel or change our FRC wide standards to conform to steel robots. But until then, the lower density of aluminum and comparable strength will make it seen lighter for FRC purposes.

Re: Advise for Galvanized Steel
 

The difference is large enough to be noticed, for purposes of FRC use.

Re: Advise for Galvanized Steel
 

Um, we are talking about galvanized steel, so the copper would be coming into contact with zinc. Go look up what happens when copper and zinc are in contact with each other. Can you say... "battery"?

You can perform electrolysis with many materials, not just water.

Thank you MrBasse for the elaboration.

My concern was not the zinc fumes, but weld spatter. Glavanized spits out molten globs of metal a LOT more than other materials.

I did not say it couldn't be welded, just that this particular person should not try it.

I stand corrected.

Re: Advise for Galvanized Steel
 

I disagree, although I will point out that stainless steel (302, 303, 304, 316) is a specific and (typically) less durable subset of steels (without getting into hardenable stainless such as 440C). The 3x price differential on stainless makes it less than desirable for teams to work with in the raw, aside from the additional tooling needed to properly work it. However, I will support my original contention with the following links and tables...

Reference #1
Reference #2

from reference #2...
........................................Aluminium. ................Steel
Density, ρ kg m−3...............2,700......................7 ,800
Young modulus, E N mm−2....70,000....................210,000
Shear modulus, G N mm−2.....27,000....................81,000
Poisson ratio, ν.....................0.33........................ 0.3

from matweb.com...
1018 steel versus 6061-T6 aluminum versus ASTM A526 galvanized steel

I could never bring myself to use aluminum for a shaft. It is too weak (comparably) to take that shock and torsion loads, as well as being more prone to unannounced catastrophic failure over steel (steel bends and then breaks ... aluminum has a much smaller deformation period before it snaps under the same loads). I'd rather use a steel shaft so that I could press-fit it into a bearing. The surface properties of aluminum just aren't good enough (at least for me) for rotating or direct-contact sliding.

Re: Advise for Galvanized Steel
 

So if I have the tooling and can keep the weight down why not save the money? And if I get 3 times as much free sheet steel wouldn't it just be better to save the money and be smart about its use?

Basically what I'm getting at is it isn't as simple as Steel is denser or aluminum is less rigid. For instance at the beginning of last build I found that a welded steel version of the kit-bot frame we used would be several times more rigid and cheaper. It would only have been about 2-5lbs heavier and that robot was 98lbs at inspection. We didn't posses the tooling to work it quick enough yet so we scraped it.

Witch metal to use has to do with the circumstances surrounding the team and the build.

Re: Advise for Galvanized Steel
 

This statement can be generalized to "material choices are context-dependent," or "design choices are context-dependent," or even "essentially all utility calculations are context-dependent." It is good to keep in mind the difference between a heuristic rule and a fundamental principal - general statements about "optimal materials for FRC" are quite clearly of the former sort, and you should thus interpret them as such.

Re: Advise for Galvanized Steel
 

I would agree that 6061 alloy aluminum is a poor choice for shafts, but 2024 alloy aluminum and particularly 7075-T6 have excellent material properties that are competitive with many steel alloys. These two aluminum alloys are much harder and have significantly higher yield strengths than 6061.

I've been using 2024 and 7075 for shafts on FRC robots since I was in college in 2010, and have never had one fail. Plus, I absolutely love machining 7075 aluminum on mills and lathes. With good carbide tools, you can machine it like a hot knife through butter, as it does not have any of the galling issues that plague softer aluminum alloys. It's my second favorite material to machine after Delrin.

// Note: I didn't directly link to the Matweb pages for 2024 and 7075 since apparently the links are tied to cookies and 404 after a while.

Re: Advise for Galvanized Steel
 

Well.... 7075 is twice as strong as certain steels, so yeah, it is "significantly stronger"

Re: Advise for Galvanized Steel
 

You're not looking at the right alloys. AndyMark steel parts are 4140 stainless with a yield strength of 60200 psi, but 7075 aluminum (vex pro parts) have a yield strength of 78,000 psi. Also, I don't really follow the shaft argument. Any 3 CIM gearbox that I've ever seen uses an aluminum shaft. Same with our climber.

Re: Advise for Galvanized Steel
 

I will totally agree that aluminum, especially 7075, machines really well. However, we have a tough time getting anything but 6061 locally. One of our former mentors went out and got some cheap aluminum from a different alloy in the 6xxx series that machined like garbage. Regardless of speed, feed, or cutter age, it rolled instead of cutting. It reached a point where I would have preferred to be cutting gummy stainless (AL6XN).

However, I digress. We've bent a number of aluminum shafts and torn up the surface of others in bearings, so we're gunshy about going that route again. I'd be interested to know what installation and mounting techniques you use for the aluminum shafts.

Whoops. :o Didn't realize that. Sorry. The short form was that the materials listed matched the chart in the post for properties and that the galvanized was not significantly different from the 1018.

Re: Advise for Galvanized Steel
 

That's possible. However, 4140 is not stainless (under AISI and ASTM coding). It is a steel which, among other things, is excellent for shafting.

Re: Advise for Galvanized Steel
 

We're all shafted now and then.:o

We've digressed significantly. I think the OP has a better idea of how to work with Galvanized Steel, and aluminum versus steel probably deserves a thread of its own. Or?

Re: Advise for Galvanized Steel
 

I don't really have a problem with a materials science class in a thread now and then. ;)

Also on the steel vs 7075 shafting thing, personally reducing drive train inertia is a priority and also reduces overall weight. Design wise I like to go a little heavy in the lower frame and keep all the scoring stuff up top light. Coupled with lightweight drive train parts and as few as possible. I can't tell you how much time I spent trying to get a 2" colsin to work so I'd only need a 4:1 of the CIMs.
PS I really like the torque/speed combo from 8:1 on 4" wheels. PSS really dislike drive train inertia.

Re: Advise for Galvanized Steel
 

This isn't as bad as the "Driver Station Power" thread. That started out with legalities of marine batteries in the driver station/battery cart, but diverted to microcontrollers, the propeller chip and comparing and contrasting it's functions.

At least this thread is still on topic.

Re: Advise for Galvanized Steel
 

What do you mean by "drivetrain inertia" in this context? Are you concerned about the moment of inertia of the output shaft of your gearbox? And if so, why?

Re: Advise for Galvanized Steel
 

I mean to say the total mass of all my moving parts and the friction between them to increase the efficiency of the drive train itself.

Re: Advise for Galvanized Steel
 

OK. Friction is a big issue in an FRC drivetrain. Inertia, not as much. They are entirely different things.